Independently moving, concentric rotating shafts may be used as part of a rotating gear train system, such as a two-way clutch system. In such arrangements, bearings may be used as a means for maintaining concentricity of the rotating shafts. Ball bearings are often used in these arrangements when said arrangement is used in an aerospace engine, such as a gas turbine engine.
Gas turbine engines, such as those used to power modern commercial and military aircraft, may employ a two way rotating gear train system including two concentric rotating shafts arranged within the engine. The inner shaft may be in operative, rotating association with a rotating element of a fan section of the gas turbine engine, such as a gear of a gear box or the fan itself. For example, the engine may include a compressor section and a turbine section. The compressor section may include a low pressure compressor and a high pressure compressor and the turbine section may include a low pressure turbine and a high pressure turbine. The inner shaft of the gear train system may interconnect the low pressure compressor and the low pressure turbine while the outer shaft of the gear train system may interconnect the high pressure compressor and the high pressure turbine.
In such designs, the bearings within the stack of components for the concentric rotating shafts require robustness and operational longevity. To achieve such robustness, the engine designer may preload the ball bearings of the bearing stacks with a preload force. Generating preload can be accomplished using a variety of methods.
Further, without the presence of preload on a bearing stack, problems may arise, such as false brinelling on an inner bearing stack due to both shafts turning as a coupled pair. Therefore, solutions are needed to provide proper preload on the bearing stacks to ensure there is always a preload force on the bearings and to create allocation for proper flow of lubrication.